The present invention relates to a humeral prosthesis.
When there is a fracture of the upper end of a humerus, the latter generally breaks into several pieces, namely the diaphysis, the humeral tuberosities and, finally, the head of the humerus which cooperates with the glenoidal cavity of the shoulder.
When such a fracture is reduced, only the humeral head has to be replaced by a substantially hemispherical dome, while the other fractured pieces may be reconstituted around a prosthesis.
It is known that such a prosthesis generally comprises a shaft, or diaphyseal portion, introduced in the humeral canal of the diaphysis of the bone. This shaft is extended by a metaphyseal portion which, with reference to a prosthesis borne by a patient standing up, is curved upwardly and inwardly, and around which the tuberosities constituting the metaphysis of the bone are grouped together, with a view to reconstitution thereof. The metaphyseal portion of the prosthesis is joined to a flange for receiving the dome replacing the humeral head.
However, this type of prosthesis presents a drawback, in that it does not allow optimum positioning of the large and small tuberosities with a view to suture thereof.
In order to overcome this drawback, WO-A-98/15241 provides a humeral prosthesis presenting means for positioning these humeral tuberosities. To that end, the zone of connection between the metaphyseal portion of the prosthesis and the flange is provided, in its outer part, with at least one rib extending, with respect to the plane of symmetry of this prosthesis, at an angle included between 20 and 40xc2x0. Such a rib, which may be divided into two, extends in the direction of the bicipital groove, in the vicinity of which the large and small tuberosities must be joined. However, such a solution is not completely satisfactory, from the anatomical standpoint, as it is not certain that the humeral tuberosities can be positioned in their natural configuration.
In order to overcome all the drawbacks of the prior art set forth hereinabove, the invention proposes to provide a humeral prosthesis allowing a precise and anatomical positioning of the large and small tuberosities to permit the suturing thereof.
To that end, the invention relates to a humeral prosthesis comprising a shaft intended to be anchored in the medullary canal of a humerus, a metaphyseal portion extending this shaft upwardly and inwardly, this metaphyseal portion being joined to a flange supporting a dome adapted to cooperate with the glenoidal cavity of the shoulder, characterized in that the metaphyseal portion comprises, in its outer part, at least one antero-posterior rib for support of the humeral tuberosities, the or each rib extending in a plane oriented at an angle included between 45 and 135xc2x0 with respect to the frontal plane of the prosthesis.
Thanks to the invention, and in particular to the orientation and dimensions of the or each antero-posterior rib, the humeral tuberosities can be reconstituted around the outer part of the metaphyseal portion of the prosthesis in a satisfactory configuration from the anatomical standpoint. In particular, the angle of orientation of the plane of the or each antero-posterior rib with respect to the frontal plane of the prosthesis may be provided to be close to 90xc2x0. This configuration proves particularly advantageous for reconstituting the humeral metaphysis.
According to advantageous aspects of the invention, the prosthesis incorporates one or more of the following characteristics:
The or each antero-posterior rib extends, from the frontal plane, with a maximum width such that its projection on a plane perpendicular to the frontal plane corresponds substantially to the distance separating the posterior edge of the bicipital groove of the humeral metaphysis with respect to a central axis of the humeral head. The width of the or each antero-posterior rib is thus adapted to the anatomy of the humeral metaphysis.
The metaphyseal portion further comprises, in its outer part, an outer median rib extending substantially along said frontal plane, the or each antero-posterior rib extending from the inner edge of said outer median rib. This configuration allows a particularly satisfactory bearing for the humeral tuberosities.
The metaphyseal portion of the prosthesis comprises two antero-posterior ribs, substantially symmetrical to each other with respect to the frontal plane. These ribs make it possible to use the prosthesis of the invention for a right or left shoulder and give this metaphyseal portion a good dimensional stability, particularly in torsion.
The metaphyseal portion comprises two branches, outer and inner respectively, defining therebetween a recess, the outer branch being provided with the or each antero-posterior rib. This recess allows osseous fusion through the metaphyseal portion of the prosthesis.
The outer branch is formed by said outer median rib and said two antero-posterior ribs. This embodiment is advantageous since it is of simple construction and it allows the prosthesis to present a wide outer surface for contact with the humeral tuberosities. In that case, the outer branch advantageously presents a T-shaped cross-section.
The free edge of the or each rib is inclined with respect to the frontal plane, the width of the or each rib increasing in the direction of the flange.